MIDBRAIN AND THALAMUS OF NECTURUS 237 



specimens is much greater than the two or three seen by Kings- 

 bury. They enter the epiphysis from each side at its attach- 

 ment to the epithalamus and then turn dorsalward through the 

 epiphyseal stalk and spread out in the walls of the vesicle. 



The study of the peripheral distribution of these fibers is 

 rendered very difficult by the presence in the epiphyseal epithe- 

 lium of granules of a lipoid substance which stains in our Weigert 

 preparations with exactly the same color as the myeUn sheaths. 

 This material is intracellular and is very abundant in the epithe- 

 lium of the pineal vesicle and less so in the dorsal sac and para- 

 physis. In the epiphysis it takes various forms as seen in 

 Weigert preparations — sometimes small deep blue granules 

 scattered throughout the cytoplasm, sometimes crowded cres- 

 centic masses of deeply stained granules closely applied to the 

 nucleus, and sometimes isolated larger deep blue granules. 

 The latter form is in some cases difficult to distinguish from the 

 myelinated nerve fibers. The nerve fibers are, however, inter- 

 cellular and under high powers of the microscope can usually 

 be recognized. They appear to be distributed throughout all 

 parts of the pineal vesicle. 



In view of the presence in the pineal sac of Sphenodon 

 (Dendy, '10) of nerve cells, which are said to give rise to the 

 right pineal nerve, I have looked for evidence of nerve cells in 

 the epiphysis of Necturus, but without success. Accordingly, 

 I am unable to say whether these nerves are afferent or efferent 

 with reference to the brain. 



The course of the parietal nerve will first be described as 

 seen in horizontal sections by the Weigert method. There are 

 three imperfectly separable roots of the parietal nerve, (1) 

 a rostral root connected with the brain in front of the haben- 

 ular commissure and observed on only one side; (2) a middle 

 root, larger than the other two and connected with the brain 

 behind the habenular commissure ; and (3) a caudal root, distally 

 associated with the second root but proximally turning caudad 

 near the mid-plane to intersect the fibers of the commissura 

 tecti diencephali. The fibers of these three roots (or part 

 of them) unite within the brain ventrally of the pars inter- 



